Trifexis As A Heartworm Preventative

Is Trifexis, A Popular Pet Medication, Safe?


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by Lorie Huston, DVM on November 17, 2013



Recently, there have been news reports making the claim that Trifexis, a medication commonly used to prevent parasites in dogs, may not be safe. One particular story tells the story of three 16 week old Vizsla puppies that allegedly died within 3 weeks of having their first dose of Trifexis.

Needless to say, this report, which has gone viral on the internet, is sparking fear among pet owners, not to mention the distribution of a great deal of misinformation.

Let’s take a closer look at this story and separate the fact from the fiction. Here’s what we know:

  • The necropsy (animal autopsy) reports for all three pups listed the likely cause of death as a bacterial infection causing heart failure. No symptoms were consistent with a typical drug toxicity. A second pathologist reviewed the necropsy reports and concurred that Trifexis was unlikely to be the cause of death. (Sources: American Veterinary Medical Association, pathology report from Engelhardt Consulting, Inc, necropsy report from University of Florida Veterinary Medical Center, and necropsy report report from University of Georgia’s Veterinary Diagnostic Laboratories.)
  • Any drug has the potential for causing side effects or adverse reactions. In most cases, the side effects attributed to heartworm prevention are mild and include things like depression, lack of appetite or even vomiting.
  • Since its release in 2010, more than 50 million doses of Trifexis have been dispensed. FDA reports show that about 3000 adverse reactions have happened with the vast majority being either vomiting or lethargy. To put it in perspective, that’s about 6 dogs in every 10,000 doses.
  • The important thing to remember is that Trifexis is a safe and effective heartworm prevention medication for the vast majority of dogs. For those pets who do experience an adverse reaction to Trifexis, other products, such as Sentinel or Heartgard, are available to insure protection against deadly heartworms and intestinal parasites.

Obviously, the deaths of the puppies is regrettable and, understandably, heartbreaking for the families involved. However, there does not appear to be a link between their deaths and the medication Trifexis. The information above is presented so that you can judge for yourself.

The following information is offered by the American Veterinary Medical Association:

“Heartworm prevention is critical to your pet’s health, so please do not stop giving your pet his or her preventive. There are several choices of medications for heartworm and parasite prevention in dogs, and [your veterinarian] can help you choose the appropriate preventive for your pet. If you have concerns about your pet’s preventive medication or would like to discuss other medication options, please let [your veterinarian] know. That’s an important conversation to have with your veterinarian. Our hearts go out to those who’ve lost their pets and who feel it may be due to a medication. It’s always difficult to lose a pet, and we know it can be even harder to lose one unexpectedly. To date, however, it’s important to note that no deaths have been definitively linked to this drug.”

Heartworms have been diagnosed in all 50 states, making preventive medication an important part of your dog’s preventive health care plan. If in doubt about whether your dog is properly protected or at risk for heartworms, consult your veterinarian. More information about heartworms and heartworm disease is available at the American Heartworm Society.

If you suspect your pet has experienced an adverse reaction associated with Trifexis or any other medication, contact the manufacturer to file an adverse event report. The manufacturer is required to provide this information to the FDA. Your veterinarian can help you document and report the adverse reaction.

If you have concerns about Trifexis or any other medication your dog is taking, talk with your veterinarian. If you are uncomfortable using Trifexis, your veterinarian can help you choose a suitable alternative.

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About Lorie Huston, DVM Lorie Huston is an accomplished veterinarian, an award winning blogger, a talented author and a certified veterinary journalist. She is available for writing assignments, blogging and social media consultation, and SEO strategy.